Basic aluminum halides, particularly the chlorides, also referred to as aluminum chlorohydroxides, aluminum sesquichlorohydrate, aluminum dichlorohydrate and the like, as well as aluminum nitrates, have been known and used for years as effective antiperspirants. They constitute the essential active ingredient in many currently marketed antiperspirants.
In general, basic aluminum halides and nitrates are complex structures comprised of mixtures of polymeric and monomeric compounds having various sizes and molecular structures, together with varying amounts of bound or coordinated water. They can be represented by the empirical formula Al.sub.2 (OH).sub.(6-x) y.sub.x, wherein x is between 0 and 6 and need not be an integer, and y is one or more of the group including chloride, bromide, iodide or nitrate ions. The empirical formula is simplified and is intended to include basic aluminum chlorides containing coordinated or bound molecules of water, as well as basic aluminum chloride polymers, complexes and mixtures thereof.
Particularly preferred compounds are aluminum chlorohydrates in which x is about 1 to 2, and most preferably x is about 1, the latter being referred to as 5/6 basic aluminum chloride. Such compounds have an Al:Cl mol ratio of about 1:1 to 2.1:1, and preferably a mol ratio of from 1.9:1 to 2.1:1.
The 5/6 basic aluminum chloride (hereinafter referred to as ACH) has been recognized as the standard active ingredient for antiperspirants for many years. It has been available in various forms, typically in 50 weight percent aqueous solution (commercially available from Reheis Chemical Company under the trademark "Chlorohydrol.RTM.") or in dry form obtained by spray drying aqueous solutions to some extent, but which does not remove all of the bound or coordinated water. These dry forms are available in different particle sizes. They are also referred to as "activated ACH" or "enhanced efficacy ACH". In addition, these compounds may be co-dried or otherwise combined with any of a number of adjuvants and/or additives designed to perform various functions, such as moieties of propylene glycol, polyethylene glycol and the like.
Basic aluminum compounds have been formulated with various materials to form aerosol spray-type antiperspirants, as well as formulations for pump sprays, creams, sticks, roll-ons and the like.
Aluminum chlorohydrates, hereinafter designated with the generic term "ACH", are the only active antiperspirants deemed safe and effective by the Federal Drug Administration for use in aerosol antiperspirant products.
The propellants used for forming aerosol-type antiperspirants up till now have been highly volatile organic compounds (HVOC), such as fluorocarbons, known collectively as Freon. However, since these fluorocarbons are believed to deplete the earth's ozone layer, the Federal Government has banned the use of Freon. Each state must outline plans for implementation of the current guidelines and set a date for compliance. The California Air Resource Board (CARB) has proposed that high volatility organic compounds (HVOC), i.e. compounds that exert a vapor pressure greater than 80 mm Hg at 20.degree. C., be 0%, and that medium volatility organic compounds (MVOC), i.e. compounds that exert a vapor pressure greater than 2 mm Hg at 20.degree. C., be 10% by Jan. 1, 2001.
Because CARB had originally mandated compliance with the above standards by Jan. 1, 1999, various manufacturers of antiperspirant aerosols attempted to switch from fluorocarbons to a mixture of ACH and 1,1-difluoroethane.
1,1-Difluoroethane has no chlorine atoms, and thus is not of concern regarding stratospheric ozone destruction by chlorofluorocarbons or other chlorinated hydrocarbons. It has an ozone Depletion Potential of zero, and the Environmental Protection Agency (EPA) has found that it is not a VOC.
Unfortunately, however, ACH and 1,1-difluoroethane react with each other over time, particularly at elevated temperatures. This reaction produces 1-chloro-1-fluoroethane (replacing one of the F ions with a Cl ion), hereinafter referred to as monochlorofluoroethane, and acetaldehyde as by-products. Acetaldehyde is classified as a toxic compound by CARB and as a hazardous air pollutant by the EPA. Further, the reaction between 1,1-difluoroethane and ACH also results in corrosion of metal containers, such as those used to store aerosol products, and in the deterioration of the valve component of the containers.
The mechanisms of these reactions is not known with certainty, or whether the generation of these by-products takes place separately or whether one leads to the other. However, their presence in the above compositions can be measured.
Thus ACH and 1,1-difluoroethane cannot be used together by themselves in antiperspirant aerosol compositions, and a search for a means of inhibiting the formation of the acetaldehyde by-product from the above combination for a period of about two years at room temperature was initiated.